NeuroradiologyMyelomeningocele
open spinal dysraphism deriving from an anomaly of neurolation resulting in
protrusion and exposure to the air of a myeloskistic spinal cord (neural placode) through a skistic
spine. The terms myelocele or myelomeningocele are used according to the degree of
herniation of the spinal content through the opening.
Embryologically myelo(meningo)cele derives from an incomplete dorsal fusion of the neural ectoderm during neurolation that also prevents the separation of the neural and cutaneous ectoderm, the inward migration of the mesoderm and, as a consequence, the closure of the posterior elements of the spine and the formation of a cutaneous covering layer.
Myelo(meningo)cele is evident at birth and requires immediate reparative surgery. Because the neural plate and meninges are anchored to the skin the spinal cord is tethered. After repair the neurological deficit remains stable.
Associated anomalies of myelo(meningo)cele include defective segmentation of vertebral bodies, hydrocephalus (almost invariably present), Chiari II malformation (also almost invariably present to variable degrees), syringohydromyelia, kyphoscoliosis (resulting from segmentation anomalies but also, most frequently, from simple neuromuscular imbalance), dermoids and epidermoids, arachnoid cysts, dorsal dermal sinus and diastematomyelia (present in up to 46% of patients).
Notably, in patients with associated diastematomyelia only one hemicord may be affected by myelo(meningo)cele (hemimyelocele) the other being normal or, more commonly, tethered by a tight filum terminale. Hemimyelocele must be suspected if neurological symptoms are asymmetrical and must be searched for with imaging as it may alter the surgical approach. Otherwise imaging is not usually indicated for myelo(meningo)cele before surgery.
Neuroradiological investigation is usually performed after surgery to assess associated anomalies and in the case of postsurgical neurological deterioration.
MR is the technique of choice and a complete study of head and spine is required. All the previously mentioned associated anomalies should be carefully searched for. Sequences on the spine should include coronal sections so that diastematomyelia is not misdiagnosed. In the case of a cystic intraspinal CSF-like mass suggesting arachnoid cyst, diffusion imaging should be performed to rule out epidermoid tumour and dermoid tumour.
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